One example of a method for analyzing characteristics of a substance is to hold a specimen on an aperture array structure, radiate the aperture array structure on which the specimen is held with an electromagnetic wave, analyze a transmittance spectrum thereof, and measure the characteristics of the specimen. Specifically, for example, a technique of radiating a metal mesh filter to which a protein that is a specimen is attached with a terahertz wave and analyzing a transmittance spectrum thereof is used.
One example of a method of measuring a small amount of specimen with high sensitivity is to radiate an aperture array structure, such as a metal mesh, with an electromagnetic wave, such as a terahertz wave. For example, Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2007-010366) discloses a method of holding an aperture array structure (e.g., metal mesh) including apertures and a specimen on a base closely adhering to the aperture array structure, radiating the aperture array structure with the specimen being held with an electromagnetic waves, detecting the electromagnetic wave passing through the aperture array structure, and thus measuring characteristics of the specimen on the basis of a change in frequency characteristic caused by the presence of the specimen.
Such a measurement method using the aperture array structure needs preprocessing, such as dropping an analyte on the aperture array structure, drying, and washing. However, it is preferred in, for example, a blood test in a medical institution that the measurement method involve no such preprocessing.
Patent Document 2 (Japanese Unexamined Patent Application Publication No. 2007-163170) discloses a method used when an analyte is liquid that contains a specimen (dissolved matter). The method is to measure characteristics of the specimen by radiating a container that accommodates both the liquid containing the specimen and an aperture array structure with an electromagnetic wave.
In the method described in Patent Document 2, the capacity of the container for accommodating the liquid and the aperture array structure is typically large, and the necessity of plenty of analyte (liquid) is a problem.
In addition, it is necessary for the method in Patent Document 2 that an electromagnetic wave, which serves as a probe, pass through two objects of the liquid including the specimen and the container. Typically, the liquid and the container reflect or absorb electromagnetic waves, and weakness of a signal of a transmitted electromagnetic wave and complication of analysis of obtained data are problems.
If the number of measurements or the number of kinds of specimens is large, the methods disclosed in Patent Documents 1 and 2 need tasks such as preparing a new aperture array structure and attaching a specimen for each measurement.
Examples of a factor for error relating to measurements can include dimensional variations in the aperture array structure. Such a factor for error has particularly a large influence if the amount of specimen is small and the change in frequency characteristic is very small. Dimensional variations in the aperture array structure increase in the order of in the same aperture array structure, among individuals of aperture array structures, and among production lots of aperture array structures.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2007-010366    Patent Document 2: Japanese Unexamined Patent Application Publication No. 2007-163170